add actions/cache support

README.md

@@ -146,3 +146,18 @@ jobs:
      - run: flutter build macos
 ```
 
+Integration with actions/cache:
+
+```yaml
+steps:
+- uses: actions/checkout@v2
+- uses: actions/cache@v2
+  with:
+    path: ${{ runner.tool_cache }}/flutter
+    key: flutter-2.5.0-stable
+- uses: subosito/flutter-action@v2
+  with:
+    channel: stable
+    flutter-version: 2.5.0
+- run: flutter --version
+```